We reveal the real skinny behind the myths that make you fat.

Big Fat Diet Lies

Big Fat Diet Lies

Ask 10 people for weight-loss advice, and you'll get 10 different answers: Work out constantly. Set a large goal. Resign yourself to winter weight gain. "Most of us have been following certain rules for how to shed pounds our entire lives," says Nancy Snyderman, M.D., chief medical editor of NBC News and author of the book Diet Myths That Keep Us Fat. "But much of what we have been told about weight loss is actually false." Here, Snyderman weighs in on the diet myths it's time to ditch — and the surprising truths that will help you get and stay slim.

THE MYTH: The more you work out, the better.

THE MYTH: The more you work out, the better.

You already know that exercise is one of the best things you can do to maintain your weight and boost your overall health, but overdoing it can actually have the opposite effect. "Working out seven days a week can weaken our immune system, strain our joints, and tire us out," Snyderman says. "Your muscles need time to repair so they can be more efficient during your next session." And if you're exercising with improper form due to fatigue, you'll actually burn fewer calories than if you were exercising correctly, she says. To prevent workout burnout, schedule at least one day off a week, and change things up a bit each session — by doing arm weights one day, say, and leg moves the next — to avoid overusing one set of muscles. Be sure to keep your back straight and not to lean on the handles of cardio equipment, to prevent injury and maximize calorie burn.